As the electronics industry advances, and production of light weight components increases, the development of new materials gives producers increased options for further improving the performance and ease of manufacture of such components. Adhesive compositions are used for a variety of purposes in the fabrication and assembly of semiconductor packages and microelectronic devices. The more prominent uses include bonding of electronic elements such as integrated circuit (IC) chips to lead frames or other substrates, and bonding IC chips to other IC chips. Adhesives useful for electronic packaging applications typically exhibit properties such as good mechanical strength, curing properties that do not affect the component or the carrier, and rheological properties compatible with application to microelectronic and semiconductor components.
The demand for smaller and more powerful electronic components presents certain challenges to the microelectronic packaging industry. One way to include more semiconductor die in a component without increasing circuit board area is to arrange the die in a stacked configuration. Indeed, “stacked die” packages conserve “circuit board real estate” without sacrificing power or performance of the electronic component. In addition, the die used in stacked die applications are becoming ever thinner, requiring new adhesive solutions in order to preserve the integrity of these very thin die.
Moreover, other configurations of computer chips on circuit board such as those that require direct attachment to a substrate or board (e.g. “Flip Chips”), required similar properties to achieve higher speed and chip density on circuit boards. Yet with high density and direct contact between circuit boards and chips, there is concern about the thermo-mechanical expansion mismatch between the chip and the substrate or board, as well as concern that moisture can cause problems with tiny solder joints.
Glycidyl ether and glycidyl ester epoxy compounds have been commercially important as components of thermoset resins and adhesives for several decades. Not only can these reactive oxirane compounds be catalytically cured to yield cross-linked thermosets by themselves, but they can also be co-cured with a variety of other compounds (which are commonly referred to as epoxy curatives).
Primary amines and phenols are among the useful curative compounds for epoxy resins. Each primary amine can react twice with an epoxy functional group, while a phenol will react once. Di-functional primary amines, therefore are useful as cross-linking curatives for epoxies, while di-functional phenols tend to produce thermoplastic segments through chain extension. Aliphatic amines are potent curatives for epoxy compounds, but are usually far too reactive to be used in one-component adhesive compositions. Compounds that contain both aromatic amine and phenol functionality are know and available in commerce. These include the relatively low cost 2-aminophenol, 3-aminophenol, and 4-aminophenol isomeric compounds. Other compounds in this commercially available category of hybrid amine-phenol epoxy curatives includes 5-amino-1-naphthol. All of these compounds have been found to be too reactive as epoxy curatives and yield one-component blends with epoxy monomers that have been found to have insufficient pot life for practical one-component applications.
The microelectronics industry continues to require new adhesives that are able to meet its varying demands. Among those demand is a need to have better curatives for epoxy resins. Accordingly, there is a need for the development of materials to address the requirements of this rapidly evolving industry. Some of the commercially available lower molecular weight hybrid amine-phenol compounds are also relatively volatile and pose a health risk to the end user via inhalation of toxic vapors during curing operations. There remains a need, therefore, for hybrid curative compounds that have better pot life, and lower volatility.